1. Field of Invention
The present invention relates to a drive arrangement for vehicles with at least two drivable vehicle axles, wherein the drive arrangement comprises at least one first motor, which is propulsively connected to a first vehicle axle, and a second motor, which is propulsively connected to a second vehicle axle. The drive arrangement according to the invention is particularly suitable for utility vehicles and agricultural tractors.
2. Description of Related Art
Utility vehicles, particularly agricultural utility vehicles such as for example a farm tractor, frequently have at least two drivable vehicle axles. Also passenger cars, which are designed to travel over wet or smooth roadways and off-road, frequently have two drivable vehicle axles. In the case of such vehicles and particularly over rough terrain all vehicle axles and thus all wheels can be driven, so that—as is generally known for all-wheel drives—traction is improved as a result.
The German Patent DE 42 09 950 C2 describes a drive for twin-axled vehicles used in agriculture and/or civil engineering. The construction of such a drive 30 is illustrated in FIG. 1. In the case of this drive an internal combustion engine 1 (or a crankshaft of the internal combustion engine) is operatively coupled via a clutch 2 to the input shaft 3 of a power-branched planetary transmission 4. The planetary transmission 4 is formed by way of a planetary gear and splits the power, delivered by the input shaft 3, into a hydrostatic and into a mechanical power branch. More particularly a first output shaft 5 of the planetary transmission 4 directly drives a differential gear 6 of a rear axle H of the utility vehicle and thereby forms the mechanical power branch. A second output shaft 7 of the planetary transmission 4 drives an adjustable hydraulic pump 10 via a gear wheel stage 8, 9 and thereby forms the hydrostatic power branch. The hydraulic pump 10 in turn drives two parallel-connected, adjustable hydraulic motors 11, 12 via (not illustrated) hydraulic lines. The hydraulic motors 11, 12 comprise output shafts 13, 14 aligned with one another in each case. The output shaft 13 of the hydraulic motor 11 drives the first output shaft 5 of the planetary transmission 4 and thus the differential gear 6 of the rear axle H of the utility vehicle via a gear wheel stage 15, 16. The output shaft 14 of the hydraulic motor 12 drives the power train 17 leading to the front axle V via a gear wheel stage 18, 19. Both output shafts 13, 14 can be coupled together by means of a clutch 20.
In DE 42 09 950 C2 the hydraulic pump 10 is adjusted as a function of the power demand, which the driver sets by corresponding movement of the accelerator pedal and/or a driving speed lever. Furthermore, driving states of the vehicle, such as for example the stationary state of the vehicle, while the engine is running, reverse and forward gear can be adjusted and changed in a simple manner by regulating the hydraulic pump. The hydraulic motors 11, 12 are governed by a (not illustrated) control unit. While the vehicle is in operation the clutch 20 is usually disengaged and the (not illustrated) control unit, according to the respective operating conditions, distributes the available drive power to the hydraulic motors 11, 12 and thus to the vehicle axles H, V.
Thus, variable rotational speed and torque distribution between front axle V and rear axle H can be achieved. Such variable rotational speed and torque distribution between front axle V and rear axle H is particularly advantageous when travelling over rough terrain and with wide steering angles of the steerable vehicle axles. Particularly the rotational speed of the output shaft 14 of the hydraulic motor 12, which drives the front axle V, must be increased when rounding tight bends, since the front wheels of the vehicle cover a greater distance than the rear wheels when rounding tight bends.
Nevertheless, when travelling over rough terrain, it may occur that the driven wheels lose their capacity to transmit tractive force and spin with extremely one-sided axle load distribution and high traction power demand. If this occurs the control unit engages the clutch 20. Thus both vehicle axles H and V are temporarily driven with a constant rotational speed ratio and up to 100% of the possible transmission output torque can be transmitted via a vehicle axle H or V. Particularly torque, higher than can be made available alone by the hydraulic motor 12, can be transmitted if required via the front vehicle axle V, with engaged clutch 20. Equally torque, higher than the sum of the mechanical torque branched off from the planetary transmission 4 and the torque supplied by the hydraulic motor 11, can also be transmitted if required via the rear axle H, with engaged clutch 20.
Furthermore it is proposed in DE 42 09 950 C2 as an additional variant that at least one power train includes an isolating clutch. A drive 40, which additionally comprises such an isolating clutch 21 in the power train 17 of the front axle V, is illustrated by FIG. 2. The front axle V can be disconnected via the isolating clutch 21 from the drive by the hydraulic motor 12 and additionally from the drive by the hydraulic motor 11 and the mechanical branch of the planetary transmission 4, with engaged clutch 20.
In the case of both drives 30 and 40 of FIGS. 1 and 2 the hydraulic motor 11, additionally to the hydraulic motor 12, can drive the front axle V via engagement of the clutch 20. Vice versa the hydraulic motor 11 can be disconnected from the axle drive of the front vehicle axle V through disengaging the clutch 20. In the case of the drive 40 additionally the front vehicle axle V can be completely disconnected from the drive by the hydraulic motors 11 and 12 through disengaging isolating clutch 21. A mode of operation, wherein the two vehicle axles V and H are only driven by one hydraulic motor 11 or 12 with engaged clutch 20, is not possible either with the drive 30 of FIG. 1 or with the drive 40 of FIG. 2.
A further drive arrangement for all-wheel drive vehicles is described in the European Patent EP 1 234 706 B1. Two hydraulic motors, of which a first hydraulic motor is propulsively connected to the rear axle of the vehicle, are also provided in the case of this drive arrangement. The second hydraulic motor can be propulsively connected to the front axle via a second clutch. The front axle and the rear axle can be coupled propulsively together through engaging a first clutch and the second clutch. The drive arrangement of EP 1 234 706 B1 also does not allow a mode of operation, wherein the front axle is propulsively connected to the rear axle and together with this can be driven by the first hydraulic motor, after the second clutch between the second hydraulic motor and the front axle has been disengaged.
Usually it is expedient with drive arrangements, as they are described in DE 42 09 950 C2 and EP 1 234 706 B1, to design one of the two hydraulic motors and/or its translation so that a large torque can be transmitted. Such hydraulic motors and/or translations are usually not designed for high rotational speed ranges and thus for high driving speeds. Particularly at high driving speeds, where lower torques are required, substantial friction and leakage losses occur if all hydraulic motors are continually connected to the front axle and the rear axle and possibly further drivable axles of the vehicle.
Therefore, the present invention is based on the object of producing a drive for vehicles with at least two drivable vehicle axles, wherein two or more axles can be driven with translation, variable to each other, in a very wide rotational speed and torque range and which additionally offers the option of ensuring that all vehicle axles are driven in an as energy-saving way as possible over the entire speed range with extremely unequal axle load distribution.
The object is solved by a drive arrangement according to claim 1. Further embodiments of the invention are indicated in the sub-claims.